9506008 Mozley This proposal is for a collaborative research project investigating the relationships between groundwater flow and diagenesis in alluvial aquifers. Geologists have long recognized the importance of groundwater in the physical and chemical alteration of sediments. However, relatively few studies have been conducted that explicitly and quantitatively account for groundwater flow. Groundwater controls on the spatial distribution of diagenetic fabrics have received even less attention. Hydrogeologists, on the other hand, are beginning to formulate quantitative models describing the spatial distribution of hydraulic conductivity. From a geological perspective, the spatial distribution of hydraulic conductivity is a result of the processes of deposition and diagenesis. Incorporating information about geological processes into quantitative models of heterogeneity requires an understanding of the relationship between the processes and the spatial distribution of hydraulic conductivity. In this study, the relationship between groundwater flow and diagenesis will be investigated in the Plio-Pleistocene Sierra Ladrones Formation, an alluvial aquifer in the Albuquerque Basin of central New Mexico. Previous work has resulted in a comprehensive understanding of the depositional and paleogeographic setting of the study area. The proposed research has two principal objectives: (1) to determine the influence of early carbonate cementation on heterogeneity, and (2) to understand the controls on the origin and spatial distribution of early carbonate cement, the main diagenetic alteration influencing permeability in the unit. The first objective is a natural extension of previous work at the study site by Davis and colleagues, investigating the relationship of depositional features to heterogeneity. The second objective builds upon preliminary work at the site that indicates a close relationship between cementation and past fluid flow conditions. The hydrological aspects of the study wil l be the responsibility of J. M. Davis (University of New Hampshire) and the diagenetic/geochemical aspects will be the responsibility of P.S. Mozley (New Mexico Tech). The study will involved mapping the distribution and orientation of cemented zones in the field, and petrographic and geochemical analysis of the cements. The principal questions addressed by the proposed research are: (1) What are the types and spatial distributions of the calcite cements? (2) What is the origin of the various types of cements? (3) What are the permeability characteristics of the different types of cemented zones? (4) Can the spatial distribution of the cements and the orientation of elongate concretions be used to infer past groundwater flow conditions in the saturated zone?
